Double density method for wirebond interconnect

ABSTRACT

A method, comprising bonding a first wire to a single die bond pad to form a first bond, bonding the first wire to a bond post to form a second bond, bonding a second wire to the first bond, and coupling the second wire to the bond post.

BACKGROUND

Increasing demand for high-performance integrated circuit (“IC”) designmay prompt an increase in the number of input/output (“I/O”) connections(i.e., bond pads) for a defined die size. An increased number of I/Oconnections currently may be accommodated with one of at least twocommonly-known techniques. In a first technique, multiple rows of I/Oconnections are staggered in which the bond pads from one row are offsetrelative to bond pads from another row. Staggered designs generallyrequire an increase in die size, and thus a staggered design presents anundesirable increase in production costs. Furthermore, additional bondfingers may be necessary to accommodate additional power and groundconnections to maintain IC functionality, thereby further increasingmanufacturing costs.

A second technique of increasing the number of I/O connections comprisesreducing bond pad size, thereby allowing a greater number of bond padsto be formed on the die. However, decreased bond pad size necessitates awirebond wire of reduced diameter (i.e., cross-sectional area of thewire). Decreasing wire diameter presents multiple disadvantages. Onedisadvantage is an increase in resistance and inductance in the wire andthus a decrease in IC performance quality. Another disadvantage isintroduced by a wire “sweeping” (i.e., moving out of place) effectduring a common molding process. To counteract wire sweeping, wirelength must be reduced, thereby increasing complexity of manufacture. Athird disadvantage may arise in dies with a staggered design and reducedbond pad size. Due to a dense bond pad pitch, bond wires may be placedclosely together, thereby increasing the risk of crossing multiplewires.

A decrease in wire diameter, which increases wire inductance, maypresent several additional disadvantages. For example, an increased wireinductance may necessitate an increase in the number of power and groundconnections needed for the IC to properly function. In turn, an increasein the number of power and ground connections may limit the amount ofdie space available for I/O connections. To maintain high performancelevels, I/O connections may be dropped to the substrate, therebyreducing available substrate routing area.

BRIEF SUMMARY

The problems noted above are solved in large part by a method that usesmultiple wires to connect a die bond pad with a bond post. One exemplaryembodiment may comprise bonding a first wire to a single die bond pad toform a first bond, bonding the first wire to a bond post to form asecond bond, bonding a second wire to the first bond, and coupling thesecond wire to the bond post.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of theinvention, reference will now be made to the accompanying drawings inwhich:

FIGS. 1 a-1 c show the formation of a wirebond between a die andsubstrate bond finger in accordance with two embodiments of theinvention;

FIGS. 2 a-2 c illustrate various processes pertaining to the bondpad-to-die connections illustrated in FIGS. 1 a-1 c;

FIGS. 3 a-3 d illustrate an alternative embodiment of formingconnections between a bond pad and a bond post;

FIG. 4 illustrates a process pertaining to the embodiments of FIGS. 3a-3 d;

FIGS. 5 a-5 d show an alternative embodiment of forming wirebondconnections on bond pads between multiple dies;

FIG. 6 shows a process that pertains to the embodiment of FIGS. 5 a-5 d;

FIGS. 7 a-7 c show another embodiment of forming wirebond connections onbond pads between multiple dies; and

FIG. 8 shows a process that pertains to the embodiment of FIGS. 7 a-7 c.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, various companies may refer to a component by differentnames. This document does not intend to distinguish between componentsthat differ in name but not function. In the following discussion and inthe claims, the terms “including” and “comprising” are used in anopen-ended fashion, and thus should be interpreted to mean “including,but not limited to . . . ” Also, the term “couple” or “couples” isintended to mean either an indirect or direct electrical connection.Thus, if a first device couples to a second device, that connection maybe through a direct electrical connection, or through an indirectelectrical connection via other devices and connections. When used as anoun, the terms “bond” and “wirebond” are intended to indicate anelectrical connection of two or more entities. When used as a verb, theterm “bond” is intended to indicate the implementation of a bond asdefined above. Further, the term “bond post” may be used interchangeablywith the term “bond finger” and/or any commonly used, synonymous term.The terms “outer die pad,” “bond pad,” “die bond pad” and/or “outer diebond pad” also may be used interchangeably.

DETAILED DESCRIPTION

The following discussion is directed to various embodiments of theinvention. Although one or more of these embodiments may be preferred,the embodiments disclosed should not be interpreted, or otherwise used,as limiting the scope of the disclosure, including the claims. Inaddition, one skilled in the art will understand that the followingdescription has broad application, and the discussion of any embodimentis meant only to be exemplary of that embodiment, and not intended tointimate that the scope of the disclosure, including the claims, islimited to that embodiment.

Presented herein are techniques to create multiple ball bonds atopexisting bonds with minimal impact on IC reliability. These techniquesincrease the number of I/O connections on a die without incurring someor all of the previously mentioned difficulties. In accordance withvarious preferred embodiments of the invention, by using Stand OffStitch Wirebond technology (“SSB”) (or other appropriate bondingtechnology) to conjoin multiple bonds and increase the total amount ofwire between these bonds, the techniques presented below substantiallyincrease the cross-sectional area of each wire connection relative tothe cross-sectional area of a single wire connection. This increase incross-sectional area of wire reduces connection resistance, improvesconnection inductance and allows an increase in the number of I/Oconnections on a fixed-size die without a loss in performance quality.

FIGS. 1 a and 1 b show one exemplary embodiment and FIG. 2 a shows aprocess associated with this embodiment. FIGS. 1 a and 1 b show an ICpackage 96 that comprises a pair of dies 100 and 102. Each die comprisesone or more outer die pads 98. The outer die pads 98 and outer die pads88 are used to provide electrical connectivity between circuitry formedon the die and devices external to the IC package 96. The IC package 96also comprises a plurality of bond posts 104. Each bond post 104 can beelectrically connected to one or more of the outer die pads 98 or one ormore of the outer die pads 88. The purpose of the bond posts is tofacilitate connections being made between external devices and the dies'outer die pads. In the example of FIG. 1 a, a wire 109 within the ICpackage 96 interconnects one of the die pads 98 to one of the bond posts104. As such, one end of the wire 109 is bonded to a die pad 98 and theopposite end of the wire 109 is bonded to a bond post 104. In at leastsome embodiments, the outer die pads 98 may be of a size such that adesired number of outer die pads 98 can be formed on the die 102.

Referring now to FIGS. 1 a and 2 a, a preferred process begins with thecreation of a low loop wirebond (block 200 in FIG. 2 a) in which thewire 109 is connected between a bond post 104 and an outer die pad 98.More specifically, a wedge bond 106 is formed on the bond post 104,thereby electrically mating the wire 109 to the bond post 104. Further,a ball bond 108 is formed on the outer die pad 98, thereby electricallymating the other end of the wire 109 to the outer die pad 98. Thus, acurrent pathway is formed between the outer die pad 98 and the bond post104. In other embodiments, any type of bond may be used for the wedgebond 106 and/or the ball bond 108. For example, a ball bond may besubstituted for a wedge bond as desired. Further, any of a variety ofloop profiles (i.e., physical wire arrangements) can be used toimplement wires of varying angles and shapes as desired.

After bonding the wire 109 in place as shown in FIG. 1 a, a second wire111 is bonded in place as shown in FIG. 1 b and described in block 202of FIG. 2 a. In at least one embodiment, the wire 111 is bonded in placewith a SSB technique or some other appropriate bonding technique. Morespecifically, the process includes forming a ball bond 110 on the bondpost 104 and forming a wedge bond 112 on top of the ball bond 108. Inthe embodiment of FIG. 1 b, the wires 109 and 111 are adhered to twoseparate locations on the bond post 104, while the wires 109 and 111 areadhered to the same location on the outer die pad 98. Further, becausetwo wires are used to connect the pad 98 to the bond post 104, thecross-sectional area of the combined wires 109 and 111 is greater thanif only one of the wires were used, effectively reducing the resistancebetween the pad 98 and the bond post 104. Because of low wire heightrequirements between dies, the disclosed technique may be useful forstacked die ICs.

FIG. 1 c illustrates an alternative embodiment in which the ends of thewires 109 and 111 that adhere to the bond post 104 are adhered to acommon location on the bond post 104 rather than, as in FIG. 1 b, twoseparate locations. The technique depicted in FIG. 1 c is also describedin FIG. 2 b and comprises creating a low loop wirebond (block 250) inwhich the wire 109 is bonded in place between bond post 104 using awedge bond 106 and the outer die pad 98 using a ball bond 108 asdescribed above and as shown in FIG. 1 a, In block 252, a ball bond orany appropriate type of bond then may be created as illustrated in FIG.1 c in which the wire 111 is bonded in place. More specifically, one endof the wire 111 is adhered to the bond post 104 by way of a ball bond110 formed on the wedge bond 106. The other end of the wire 111 isadhered to the outer die post 98 by way of a wedge bond 112 formed ontop of the ball bond 108.

FIG. 1 d illustrates yet another alternative embodiment nearly identicalto the embodiment presented in FIG. 1 c with the exception of anadditional wire 113 bonded to the bond post 104 and the wedge bond 112.The technique depicted in FIG. 1 d is also illustrated in FIG. 2 c andcomprises creating a low loop wirebond (block 276) in which the wire 109is bonded in place between the bond post 104 using a wedge bond 106 andthe outer die pad 98 using a ball bond 108 as described above and asshown in FIG. 1 a. In block 278, a ball bond 110 or similar bond (e.g.,a SSB technique) then may be created as illustrated in FIG. 1 c, inwhich the wire 111 is bonded in place as described above. In block 280,one end of a wire 113 is adhered to the bond post 104 by way of a wedgebond 116. The other end of the wire 113 is adhered to the outer die pad98 by way of a ball bond 114 formed atop the wedge bond 112, asillustrated in FIG. 1 d. In this way, the cross sectional area of wireconnecting the outer die pad 98 and the bond post 104 is greater than ifonly one of the wires was used, substantially reducing wire inductance,improving conductivity and reducing IC design and manufacturing costs.In this way, performance may be improved by bonding any number of wiresto the outer die pad 98 and the bond post 104.

Another such technique is illustrated in FIGS. 3 a-3 c, with FIG. 3 abeing generally duplicative of FIG. 1 a for ease of following thediscussion below. FIGS. 3 a-3 c each show an IC 96 comprising aplurality of bond posts 104 and a die 100 stacked atop a die 102comprising multiple outer die pads 98. The technique depicted in FIGS. 3a-3 c is also illustrated in FIG. 4 and comprises establishing a ballbond 302 on the outer die pad 98 and removing the wire attached to theball bond 302 (block 400). In block 402, a ball bond 304 may be formedon the bond post 104 and connected to a wedge bond 310 formed atop theball bond 302 by way of a wire 303, as illustrated in FIG. 3 b. In block404, a wire 305 may be adhered to the bond post 104 by way of a wedgebond 306 and to the outer die pad 98 by way of a ball bond 308 formedatop the wedge bond 310. As previously mentioned, the scope ofdisclosure is not limited to the types of bonds described above. Bondtypes may be freely interchanged as desired. For example, in anotherembodiment, block 404 may comprise electrically connecting the bond post104 and the bond pad 98 by way of a wire 305 bonded to the bond post 104with a ball bond and bonded to the wedge bond 310 with any type of bond(not shown).

In an example, the outer die pad 98 is of a size such that a maximum ofa 0.8 mm diameter wire can be bonded to the outer die pad 98. A wirewith a diameter greater than 0.8 mm generally would not be used, becausesuch a wire may touch neighboring wires or outer die pads 98, causing ashort circuit and compromising the functional integrity of the IC 96.Because a 1 mm diameter wire is considered to be a standard size wire,the thinner 0.8 mm diameter wire has a greater inductance than thestandard size wire. However, implementing any of the techniquesdescribed above causes the total cross-sectional area of wiresconnecting the outer die pad 98 to the bond post 104 to be greater thanthe cross-sectional area of a single wire connecting the outer die pad98 to the bond post 104. Thus, the overall inductance of the wires maybe equal or superior to the inductance of the 0.8 mm wire or even the 1mm wire. Similarly, the resistance of the wires may be substantiallylower than the resistance of a single wire, thereby allowing a greateramount of current to be transferred between the outer die pad 98 and thebond post 104.

The techniques disclosed herein are not limited to bonding die bond padsto bond posts. Such double-bonding techniques also may be applied towires connecting die bond pads to other die bond pads, as illustrated inFIGS. 5 a-5 c. FIGS. 5 a-5 c each show an IC 96 comprising a die 100stacked atop a die 102. The die 100 comprises a plurality of outer diepads 88 and the die 102 comprises a plurality of elongated outer diepads 99. The technique depicted in FIGS. 5 a-5 c is also illustrated inFIG. 6 and comprises forming a ball bond 500 on an outer die pad 88 andremoving the wire attached to the ball bond 500 (block 600). In block602, a wire 603 is adhered to the outer die pad 99 by way of a ball bond502 and to the outer die pad 88 by way of a wedge bond 504 formed on topof the ball bond 500, as shown in FIG. 5 b. In block 604, a wire 605 maybe adhered to the outer die pad 99 by way of a ball bond 506 formed atopthe outer die pad 99 and to the outer die pad 88 by way of a wedge bond508 formed atop the wedge bond 504, as illustrated in FIG. 5 c. In atleast some embodiments, any number of wires may be bonded or otherwiseelectrically connected to the outer die pad 88 and the outer die pad 99.The scope of disclosure is not limited to the types of bonds previouslydiscussed; bond types may be interchanged with any of a variety of bondtypes as desired.

Another die-to-die double-bonding technique is illustrated in FIGS. 7a-7 c. FIGS. 7 a-7 c each show an IC 96 comprising a die 100 stackedatop a die 102. The die 100 comprises a plurality of outer die pads 88and the die 102 comprises a plurality of outer die pads 98. Thetechnique depicted in FIGS. 7 a-7 c is also illustrated in FIG. 8 andcomprises bonding a SSB ball bond 700 or other appropriate bond to anouter die pad 98 of a die 102 and removing the wire, thus leaving onlythe ball bond 700 on the pad 98 (block 800). A second ball bond 702 thenis bonded to an outer die pad 88 of a die 100 and is electricallyconnected by way of a wire 706 to a wedge bond 704 formed atop the ballbond 700 (block 802). Finally, a ball bond 708 is bonded to the ballbond 702 and is electrically connected by way of a wire 712 to a wedgebond 710 formed atop the wedge bond 704 (block 804).

The subject matter disclosed herein may be applied to a single die ormultiple dies. While the above embodiments describe specific types ofbonds, any type of bond may be substituted for a particular bond (e.g.,a ball bond substituted for a wedge bond). All bonds and double bonds,described above, may be created using any bonding technique, such as SDwirebond loops and any variations thereof (e.g., all low-loop andultra-low-loop bond techniques comprising SSB bonds, wedge bonds, ULbonds, escargot bonds, FJ loop bonds and folded loop bonds). Forexample, a wedge bond described above may be replaced with an escargotbond. The above discussion is meant to be illustrative of the principlesand various embodiments of the present invention. Numerous variationsand modifications will become apparent to those skilled in the art oncethe above disclosure is fully appreciated. It is intended that thefollowing claims be interpreted to embrace all such variations andmodifications.

1. A method, comprising: bonding a first wire to a single die bond padto form a first bond; bonding the first wire to a bond post to form asecond bond; bonding a second wire to the first bond; and coupling thesecond wire to the bond post.
 2. The method of claim 1, wherein couplingthe second wire comprises bonding the second wire to the second bond. 3.The method of claim 1, wherein bonding comprises using Stand Off StitchWirebond technology (“SSB”).
 4. The method of claim 1, wherein couplingthe second wire comprises bonding the second wire to the bond post. 5.The method of claim 4, further comprising bonding a third wire to thebond post and the bond formed by bonding the second wire to the firstbond.
 6. The method of claim 1, further comprising: prior to bonding thesecond wire, removing at least some of the first wire; bonding thesecond wire to the first bond to form a third bond; bonding the secondwire to the bond post; and bonding a third wire to the bond post and thethird bond.
 7. The method of claim 6, wherein bonding comprises formingany of a group of bonds comprising wedge bonds, ball bonds, loop bondsand folded loop bonds.
 8. The method of claim 1, further comprisingelectrically connecting the first bond to the bond post using three ormore wires, each wire electrically connected to the first bond and thebond post.
 9. A method, comprising: bonding a first wire to a first diepad to form a first bond; removing at least a portion of the wire;bonding a second wire to a second die pad to form a second bond; andbonding the second wire to the first bond to form a third bond.
 10. Themethod of claim 9, further comprising bonding a third wire to the secondbond and the third bond.
 11. The method of claim 9, further comprisingelectrically connecting the second bond and the third bond using threeor more wires, each wire electrically connected to the second bond andthe third bond.
 12. The method of claim 9, wherein bonding comprisesusing SSB. 13-24. (canceled)